A variety of different products are known which require wrapping of windings around a core member having an opening therein. Example of such products include electromagnetic sensor equipment and electrical transformers. Such products typically include a cylindrical shaped metal core having electrically conductive wires wrapped around the core.
As the conductive core and the electrically conductive wires typically must be isolated, the wires in such products are often coated, for example, with a varnish or other insulating coating. However, it is often desirable, for manufacturing and/or performance reasons, to utilize a sharp edged core with right angle interfaces at each of the outer and inner corner surfaces of the core around which the wires must be wrapped. These edges may cut into the wiring and undesirably introduce an electrically conductive path between the core and the wrapped wiring. Accordingly, various approaches have been proposed for protecting the wrapped wiring.
In one prior art approach, a non-conductive paper is placed around the core before the wire is wrapped around the core. For example, sheet cardboard may be cut to provide two circular portions with outer diameter and inner diameter values selected to correspond to the end faces of the core. A first and second rectangular strip are also cut with lengths corresponding to the circumference of the core at the respective outer diameter of the core and the diameter of the opening in the center of the core through which the wires will pass and a width corresponding to the width of the core between its end faces. These four pieces are then positioned around the outer surface of the core and taped in place. The wire (typically ranging from about 8 AWG to about 32 AWG) may then generally be safely wrapped around the core without damaging the insulating coating (for example, varnish) of the wire. However, due, in part, to the variety of different diameters (typically about 4 inches (10.16 centimeters) to about 44 inches (111.76 centimeters)) and widths (typically about 1.25 inches (3.175 centimeters) to about 8.5 inches (21.59 centimeters)) of the cores, a great deal of waste is typically encountered using the non-conductive paper wrapping. For example, the cut out of the center of the rings for the end pieces must, typically, be scrapped along with the outer portions of the material after the end pieces are cut out. The taping operation provides additional expense in materials and labor as well.
An alternative approach has been proposed in which a 90 degree plastic extrusion with two equal length sides is placed over the corners of the core. However, a problem with this approach is the tendency of the material to have uneven sides due to the wrapping of the extrusion around the circumference of the core, particularly on the edges of the inner opening of the core. This problem may be particularly acute for smaller diameter cores. In addition, an overlap of the ends of the extrusion to complete the wrap of the circumference without leaving any exposed sharp edges would result in an undesirable bump on the surface which, like the rippling caused by the wrapping of the extrusion into a circular configuration, could adversely affect performance of the finished electromagnetic product.